The present invention relates to a radiotelephone system of the type having a main transmitting/receiving device and a control transmitter unit remote from the device and provided with operating keys, a channel indicator device, a function indicator device and a loudspeaker-microphone device.
Apparatus of this type having a control transmitter unit which includes a remote control is already known in the art, as described, for example in Service Instructions KF 80/160/450, published by ROBERT BOSH GmbH in 1968, in which the connection with the radiotelephone, usually disposed in the trunk of an automobile, is established via a long, multiconductor cable which is difficult, and therefore expensive, to install.
Additionally, ultrasonic or infrared remote control transmitters are known for controlling electronic entertainment instruments, such as radios, TV's, etc., but only for conducting information in the direction from the remote control transmitter to the instrument, without it being possible for the transmitter to receive return information from the instrument.